6.8x45mm Kramer Urban Combat Cartridge (UCC) for Urban Warfare Ops

DefenseReview has covered the 6.8 SPC (a.k.a. 6.8 Remington SPC a.k.a. 6.8x43mm SPC a.k.a. 6.8mm Remington SPC a.k.a. 6.8mm SPC) round for quite some time now. We’re a proponent of the cartridge, due to its superior efficacy over 5.56x45mm NATO (5.56mm NATO)/.223 Rem. within its (6.8 SPC) operational envelope of 400-500 yards, its grassroots-level development history, and the support it’s garnered inside the U.S. Army Special Forces (SF) community and general SOCOM/Special Operations (SPECOPS) community.

Developed by elements within U.S. Army 5th Special Forces Group (Airborne) a.k.a. 5th SF Group a.k.a. “5th Group” (with help from private industry like Precision Reflex, Inc., Remington Ammunition, Hornady Manufacturing, etc.) in order to achieve significantly-enhanced terminal ballistics over 5.56mm NATO for close quarters battle (CQB) a.k.a. close quarters combat (CQC) and short-to-medium-distance engagements, the 6.8 SPC’s total development cost was approx. $5,000 (total development cost). This is according to one of the SF developers, who also happens to be a contact of ours. Understand that the 6.8mm SPC cartridge was developed totally outside the normal U.S. military small arms and ammunition development and procurement process that’s currently ruled over by the U.S. Army Infantry Board Fort Benning, GA, Picatinny Arsenal/JSSAP (Joint Service Small Arms Program), and Naval Surface Warfare Center (NSWC), Crane Division. Because of this, the 6.8 SPC has been met with considerable resistance from the U.S. Army hierarchy, putting the cartridge’s future in jeopardy.

In Defense Review’s experience so far, any/all SF/SpecOps assaulters/operators that have tested or utilized 6.8 SPC have been…

One of our contacts in 5th group told us that when he and his unit have been in combat, they feel under-gunned/under-powered with 5.56mm weapons, and he’s notices that the operators carrying 7.62x51mm NATO (7.62mm NATO)/.308 Win. M14/M1A rifle/carbines carry themselves very differently than their 5.56mm AR-carrying counterparts. M14/M1A gunners, in his experience, are generally more confident and aggressive in combat. The larger round gives them not only an combat-operational edge, but also a psychological one. This, of course, was one of the reasons why he wanted to develop a larger-caliber, harder-hitting assault rifle cartridge like the 6.8mm SPC that essentially splits the difference power-factor and size-wise between the 5.56mm NATO and 7.62mm NATO cartridges.

To utilize 6.8 SPC in his AR carbine or SBR/subcarbine (AR-15/M16, M4/M4A1, Mk18 MOD 0 CQBR, HK416, etc.), the operator can either employ a dedicated 6.8 upper receiver or convert their existing 5.56 AR upper by swapping out the barrel, bolt, and magazine to 6.8 SPC versions, and they’re off and running and gunning. Larger M4/M4A1 feedramp cuts can also be cut. The same AR-15 lower receiver is used.

Well, now there’s a new 6.8mm assault rifle cartridge being made by Kramer Defense (KD), a Division of Kramer Cartridge & Carbine LLC (KCC), that gives approximately the same or similar performance as the 6.8 SPC without having to go to a modified .30 Remington case. It’s called the 6.8x45mm Kramer Urban Combat Cartridge (UCC) a.k.a. 6.8mm Kramer UCC a.k.a. 6.8 Kramer UCC and it utilizes a standard 5.56x45mm NATO cartridge case. DefenseReview first became aware of the 6.8 Kramer cartridge at SHOT Show 2008 when we ran into Larry Kramer in the tents outside of Oakley Eyewear’s booth. Mr. Kramer handed us an inert round, and explained to us that he could safely achieve roughly the same velocity as the 6.8 SPC, which surprised us. Kramer claims that he can safely get a 115-grain (115gr) Hornady OTM 6.8x45mm Kramer UCC bullet up to 2500 fps (feet per second) out of a 16″ 1/11-twist Krieger barrel, and has done so in tests. Kramer’s firing test results comparing the 115gr OTM 6.8mm Kramer cartridge to 62gr SS109/M855 ball 5.56mm NATO and 123gr 7.62x39mm Russian ball are below. Kramer achieved 2440 fps out of a 14.5″ Krieger barrel with the same Hornady 6.8 OTM round.

About a year and a half ago, Kramer was averaging 2550 fps out of a Precision Reflex, Inc. (PRI) 6.8SPC AR upper with Silver State Armory (SSA) ammo utilizing a 115gr Remington FMJ boattail round. In a recent article that Kramer read in Guns & Ammo Book of the AR-15, titled “Barrett’s REC7 Battle Rifle”, author David Kenik got 2500 fps out of a 16″-barreled 6.8 SPC Barrett REC7 gas piston/op-rod-driven carbine with SSA ammo utilizing a 115gr Sierra OTM bullet, so SSA might have down-loaded the cartridge since Kramer tested it (unverified/unconfirmed). In any case, Kramer is achieving comparable velocities to 6.8x43mm SPC with the 6.8x45mm Kramer.

We should perhaps note that we ran into one of the SSA guys at the Land Warfare Resources Corporation (LWRC) booth at SHOT Show 2008, and he was very friendly and helpful with information about the 6.8mm SPC ammo they’re manufacturing. SSA was sharing LWRC’s booth space. DefenseReview has heard some very good things about SSA’s 6.8 SPC ammo, lately.

So, why go to 6.8x45mm Kramer UCC instead of 6.8x43mm SPC? Well, first, you get comparable muzzle velocity and energy. And, since the 6.8 Kramer UCC utilizes a standard 5.56mm NATO cartridge case, you only have to change out the barrel and mags on your AR. Unlike the 6.8x43mm SPC, you don’t have to swap out the bolt. Regarding standard 5.56mm NATO AR-15/M16 mags, according to Kramer, MagPulPMags can be modified easily to feed the 6.8 Kramer reliably, and once the mag is modified, it will still feed 5.56x45mm NATO ammo just as reliably as before the modification. Kramer is going to have aluminum mags made for his cartridge. With the 6.8 Kramer UCC cartridge, you should also be able to use Mil-Spec M249 Squad Automatic Weapon (SAW) ammo links, meaning that the 6.8x45mm should be able to be fired from a FN M249 SAW/LMG or FN Mk46 MOD 1 LMG/SAW by simply swapping out the barrel, which is a relatively minimal modification. Bottom line, you only have to swap out the barrel of your assault carbine/SBR (M4/M4A1 Carbine, Mk18 CQBR MOD0 SBR/subcarbine, or HK416 Carbine or SBR) or LMG/SAW (FN M249 SAW or Mk46 MOD1), and swap out your AR mags. Mr. Kramer points out that you can standard 5.56mm stripper clips, bandoliers, and U.S. military ammo storage cans. 6.8 Kramer adds 5.75 lbs to a U.S. military standard 840-round 5.56x45mm ammo storage can.

The following is from a document we received from Larry Kramer on 6.8x45mm Kramer UCC and 6.8x43mm SPC vs. 5.56x45mm NATO/.223 Rem. that contains comparison data on cartridge performance (muzzle velocity and energy) of 115gr 6.8x45mm Kramer UCC, 62gr 5.56x45mm NATO, and 123gr 7.62x39mm Russian respectively out to 500 yards. Mr. Kramer conducted the testing, himself.

The 6.8 X 45 Kramer UCC shoots the same 115 grain bullet as the 6.8mm SPC cartridge, the SPC gets a velocity of around 2550 fps from a 16” carbine. Currently the best velocity of the 6.8 X 45 UCC cartridge is 2500 fps from a 16” carbine. The components are still being refined and we expect to get between 2550-2600 fps when production ammunition is released.

· More energy delivered, approximately 35% increase over the 5.56mm round.
· Operates at lower chamber pressure than the 223/5.56 NATO
· Operates at cooler temperatures
· Slower cyclic rate of fire, approximately 675 RPM, compared to 875 RPM for the 5.56 NATO M855 from a 14.5” BBL.
· Barrels last twice as long

6.8 X 45 mm Kramer UCC advantages over the 6.8mm SPC:

- The 6.8 X 45 mm Kramer UCC uses the same AR15/M16 bolt as the existing 223 Remington / 5.56 mm NATO cartridge. The 6.8mm SPC uses a modified AR15 bolt with an enlarge bolt face, which can only be used for the SPC cartridge.
– The 6.8 X 45 Kramer magazine holds the same number of rounds in the magazine as the 223/5.56 mm. The 6.8mm SPC magazine that is the same physical size as a standard 30 round 5.56mm magazine only holds 25 rounds, reducing the combat load of the individual war fighter.
– Magazines designed for the 6.8 X 45 UCC can also be used for the 223 Remington / 5.56 mm NATO cartridge. Magazines for the SPC cartridge can only be used for that specific cartridge and will not function with 223/5.56mm ammunition.
– Military ammunition supply system components remain basically the same, as the 6.8 X 45 Kramer UCC uses the same stripper clips; spoons and bandoleers, even the round count per can is the same. The increase in weight of an 840 round can is approximately 6.25 pounds.
– The M249 SAW machinegun can be adapted to the 6.8 X 45 Kramer UCC cartridge with only the change of a barrel, as it can use the same links and bolt as the existing 223 / 5.56mm NATO cartridge. At this time we are not even sure it the M249 SAW could be modified to function in the SAW, but if it was possible the cost would be rather high.

Always on the lookout for a more powerful cartridge for the AR15 rifle, I was very interested in the 6.8 mm SPC when it first came out, and like many others, when I discover something new I wait to see how it evolves before I go out and buy one for myself. Being a hand loader for the past twenty plus years and an occasional match shooter, obtaining ammunition for the AR15 with bigger bullets was not difficult. Even with the heavier .22 caliber bullets I was still not satisfied with the .223 Remington cartridge as a defensive round, for recreational shooting and plinking it was ok, but as others have stated, it just does not feel like you are shooting a powerful enough cartridge when you pull the trigger on an AR15.

While reading the occasional articles about the 6.8 mm SPC I came across an article around October or November of 2005, stating that the original velocity of the 6.8 SPC was 2800 feet per second from a 24″ bolt action rifle, and that it had a chamber pressure too high for the 55,000 psi limit of the AR15/M16, so Remington reduced the target velocity by 200 feet per second, which meant the powder charged was reduced from the original loading. When I read this I began wondering if their new reduced charge would be an easier fit into the existing 223 Remington case, so I set out to see if it was possible. Most everything I had read about the 6.8 SPC was positive and those who had shot it really liked it. The main drawbacks were that it required a different bolt and magazine, and I knew if I could obtain the same velocity from a standard 223 Remington case with the same bullet it would be worth the effort to develop. If you could have the increase performance of the 6.8 SPC without some of the expensive changes it required, why would someone not want to opt for the less expensive cartridge.

Another thing I liked about my cartridge design was that it was easily obtainable, except for the powder. Anyone who reloads could make the brass easily from standard 223 Remington brass, and buy the bullets already on the market; all they would need is a powder and a barrel. Other guys like me could try this new round without spending a lot of money to see if they liked it, from using existing components already on the market. They could even use their fired 223 cases that every AR15 shooter has on hand, and make their own ammunition. Reforming new 223 brass is easy and is what I have been doing, but to use fired 223 brass would require resizing dies, so I sent off the required fired cases and had dies made for this new round so the average shooter could order them and make their own ammunition.

Being an experienced reloader and match shooter and understanding the rules and limitations of reloading I felt comfortable taking on this new project. Starting with a Redding neck expander I necked up new Winchester brass and then worked out what would be the best overall length for the new case. I made some prototype rounds and started asking around about reamers, I then decided on one company and they made a reamer from my prototype cartridges. I then obtained a 6.8 caliber barrel and had it chambered with my reamer, the result was a 20″ finished AR15 barrel with a standard rifle length gas system. Knowing the standard length gas system for a twenty inch rifle would not reliably cycle the action, my initial goal was to see if I could obtain velocities at or near that of the 6.8 SPC.

I browsed through my loading manuals and came up with a list of powders that I thought might work well; I then formed some brass, loaded some ammo and headed to the range with my chronograph. Since this was a new cartridge and there was no previous load data, and this was all from scratch, like a good hand loader I started with somewhat small powder charges to avoid any mishaps. The initial loads were slow and the bolt had to be manually cycled for each shot. Working through my initial selection of powders I realized the limited case capacity of the 223 would be my biggest challenge, but that was expected. After increasing the powder charges and changing primers and reaching maximum allowable compressed powder charges with all available powders, it seemed like I was not going to reach my goal of 2500 feet per second.

Then I obtained an older (7 years old) one pound sample can of AA2230 from my brother. It was an eye opener, by the time I reached the maximum charge of AA2230 I had obtained over 2600 feet per second from my 20″ AR15, I was ecstatic. Although I was still having to manually cycle the bolt I was making progress. I obtained a higher velocity than I had expected, had not blown the primers, and most of all, had discovered that you could send a 6.8mm 115 grain bullet over 2600 feet per second from a standard 20″ AR15 rifle. With this new discovery in hand and reviewing the potential this cartridge could have, I called a friend of mine who is an attorney and he referred me to a patent attorney he knew, several weeks later I had my first of which would become several patents filed and on the books.

I obtained several other barrels from the same manufacturer who had made them up earlier for the SPC cartridge, but as interest died off after the lack of available ammunition for the SPC, the barrels I was told were just sitting on the shelf, which was good for me. The bad news was that they were not looking at making any more like these unless it was a large special order, as there was no demand for the 6.8/.277 caliber barrels.

My next barrel was also a 20″ AR barrel and made with an “intermediate length” gas system they were using on the 6.8mm SPC, I figured I’m shooting the same bullet at around the same velocity so the intermediate length gas system should work well for my project too. I ended up with a 20″ and 16″ finished length barrel for my AR15, the 16″ used the standard carbine length gas system found on the shorter barreled AR15 223 rifles. Using the new gas system length solved the cycling problem with some but not all powders, as the pressures peak at different times with all of them, but it did reliably cycle the action with several powders, things were looking up.

Having shot almost all of the AA2230 powder that was loaned to me I tried to obtain some more, which I did, but the new AA2230 was not even close to the original, the maximum charge I could get into the case was two grains less and the velocity was much lower. Calling the people who handle the AA2230, I discovered there was no way to get the older “mix” I had been using, so that was the end of my magic powder, so I continued testing other off the shelf powders.

I was also wondering what the pressures were of the rounds I was testing, reading fired primer and brass case conditions only told me if I was getting excessive pressure, no what I was actually getting. A brief discussion at the 2006 Shot Show with a couple of powder and ammunition companies revealed it would cost an enormous amount of money to have my rounds tested, and they were all located far away. My brother had an Oehler chronograph and really liked it and told me they made other ballistic recording programs and systems. I went to their website and read about their model 43 personal ballistic laboratory, after talking to them on the phone I was told that their model 43 would get me within 2500 to 3000 psi of the actual pressure I was getting, using a strain gauge glued to the bottom of the barrel. The best thing about this system is that I could test all of the ammunition I wanted to after the initial purchase, and it would be accurate enough for my project.

I ordered the Oehler Model 43 PBL [made by Oehler Research, Inc.] and build a Remington model 700 bolt action rifle to use with the system. I then retested many of the loads I had already tested and found my pressures were rather low and well within the 55,000 psi (pounds per square inch) maximum I was held to, I only had two loads that were over that limit and they were no longer tested. All loads from this point would be tested for pressure, velocity, and function in the newly designed AR15 barrels. Also being in need of a comparison rifle, I built a 16″ 6.8mm SPC upper receiver from components from Precision Reflex Inc. The people at PRI were quite helpful in assisting me in building my upper receiver group and answered all of my questions relating to the SPC, and I found out later that PRI not only assisted in development of the SPC, but fixed many guns that were having problems with that cartridge from other manufacturers.

During my testing I did blow several primers with a couple of different powders, but not from just the powder charge being to large. When doing this kind of testing you look very closely at each round fired and watch for anything that does not feel or seem right, so when a primer blows it catches you attention, especially when you have fired this test round before and had no problems. I had been using Hornady bullets in my initial testing and they became too expensive, so I bought the Remington 115 grain full metal jacket bullets in bulk. The Remington bullets were open at the base and not enclosed in copper like the Hornady bullets, I also used Sierra bullets in my testing but the majority of the testing was with the Remington bullets.

When a primer blows you open the rifles action and check everything out to see what caused the problem and to see if anything is damaged, it was then I noticed laying in the bottom of the receiver a small ring of copper, nothing else was found to be wrong so I continued shooting. I had this happen several times in a one month period in my AR15 and one time in my bolt action rifle, when it happens in a bolt action rifle you can feel the resistance when closing the bolt and it gives you a warning that something is not right. When extracting the cartridge that the bolt was closing on I noticed the small ring of copper around the neck of the bullet, it had been left in the chamber from the previously fired round. When discussing this situation with ammunition people I discovered they had encountered the same problem. It can be caused by too soft of lead in the bullet and or too quick a build up of pressure in the case and chamber. Either way it results in the bullet being slightly deformed or bulged when the pressure builds behind the bullet, the bullet is then swaged through the chamber neck shaving off this ring of copper. This ring of copper left in the chamber causes the next round to be forced into the chamber and is actually wedging the bullet into the neck of the chamber, it takes increased pressure to dislodge or fire the bullet and in turn blows the primer due to the excessive pressure. I had never run across this situation in any of my previous reloading experience, but was glad to know others had encountered this same situation and that it was not my new cartridge that was to blame.

Once the gas system was corrected and the rifle began to cycle regularly, I then realized I would need to focus on the magazines as well, as most of the shooting up until now was just single loading, and not feeding multiple rounds from a magazine. I used 20 and 30 round magazines for my testing; I quickly discovered that after loading either magazine halfway I met increased resistance, mainly because the neck of my round was larger than the 22 caliber bullet used in the 223 Remington. The forward stiffing groove in the magazine that makes contact with the neck of the cartridge was forcing my cartridge with the larger neck in towards the center of the magazine, basically forcing the rounds into each other at the front. After loading 15 or 16 rounds into a 30 round magazine it started binding up any additional rounds being loaded, the magazine could be loaded with 28 rounds and fired, once the first round was chambered the magazines would most often function ok. With a 30 round magazine loaded with 28 rounds the first round would not chamber on the release of the bolt, but would go halfway into the chamber and stop going up at an angle, pulling the charging handle back a second time will fully chamber the round, after the first round was chambered the others would feed normally during firing, even on full auto testing.

Several attempts at modifying the existing 30 round magazine to accept my new round failed and it was obvious the magazine would need to be redesigned to be reliable with this new round. So the second patent was filed for a newly designed magazine. I later discovered a good magazine on the market that I could modify easily. All of the magazines I had tried so far were metal, aluminum magazines, I now had a 30 round P-Mag made by MagPul Industries, with which I had no previous experience. I first tried them in my 223 rifles and liked them, removing the floor plate revealed a small plastic ridge toward the front where the forward stiffing groove is on the metal magazines, being plastic it was much easier to modify than the metal magazines.

Much to my delight, by removing approximately half of the height of the plastic ridge from inside the magazine the magazine held a full load of my new cartridge and functioned flawlessly. Another idea I had thought about but was not sure would work until I had a magazine modified to function correctly with my cartridge is, would my modified magazine also feed .223 ammunition without a malfunction? The modified P-Mag worked fine with both the 6.8 X 45 Kramer cartridge and standard .223 Remington ammunition, which I believe is another plus for this new cartridge, the “6.8 X 45 Kramer”, as magazines designed for it will also function using 223 ammunition.

Having tested most of the off the shelf powders that were potential candidates for this cartridge, I discovered a pattern. Some powders would give great velocity but not function or cycle the action, and powders that would cycle the action did not give adequate velocities, due to the varying pressure curves of the various powders. Having run out of test powders, I decided I would try the same powders used by the manufacturers loading the 6.8 mm SPC. The only way to do this was to buy loaded ammunition, pull the bullets and save the powder. By doing this I discovered several powders that worked well in my cartridge. Although I did not know what the powders were, it was obvious there were powders out there that would make this cartridge perform like I wanted it to. What I also discovered when testing powders from loaded SPC ammunition, was that I could get the same or slightly higher velocity of the factory loaded SPC ammunition with a smaller charge of the same powder they were using. To me that seems like a more efficient cartridge.

While I like the 6.8 mm SPC and feel it fills a gap in the performance deficiency of the AR15 rifle, there are several reasons we feel the “6.8 X 45 Kramer” is a better choice. First is the bolt. The 6.8 SPC requires changing or modifying the bolt face of the existing AR15 bolt to accommodate the larger SPC case head, which means it will not work with the standard .223 Remington, as is therefore specific to the SPC cartridge. The 6.8 X 45 Kramer uses a standard AR15 bolt. Next is the Magazine. The SPC requires a magazine specific for that cartridge. The magazine designed for the 6.8 X 45 Kramer will also accommodate the standard .223 Remington cartridge, making it more versatile than the SPC magazine. The SPC magazine that is the same size as a 30 round .223 magazine only holds 25 rounds, which means the standard load carried by the troops would be reduced. The magazine for the 6.8 X 45 Kramer carries the same number of rounds as the 5.56mm magazine, which means the load carried by the troops would remain the same, thirty rounds in a thirty round magazine.

Other components to be considered, while not of a concern to civilians and most law enforcement agencies, are the components of the militaries ammunition supply system. The military gets its ammunition packaged in stripper clips, spoons, bandoleers and ammunition cans. Because the 6.8 X 45 Kramer uses the existing 5.56mm NATO case, all of the ammunition packaging would stay the same, even the count per can would stay the same, although the can weight would increase because of the bigger bullets. The 6.8 SPC has a larger case head, which would require changing the stripper clips and bandoleers, and the number of rounds per can, would be reduced also. These changes would be costly and therefore make the SPC less desirable as compared to the 6.8 X 45 Kramer. Another target for the 6.8 X 45 Kramer is the M249 Squad Automatic Weapon or SAW, which currently fires the 5.56mm NATO round. With only the change of a barrel the M249 could be changed over to the 6.8 X 45 Kramer, increasing it’s firepower up to thirty percent.

The results of this testing over the past two years has resulted in the 6.8 X 45 Kramer producing just over 2500 feet per second from a 16″ barreled AR15 carbine. While the cartridge and its components are still being refined before production ammunition is made, we are confident we will obtain close to 2600 feet per second from a 16″ barrel. After adjusting the chamber/reamer design several times, experimenting with barrel twist and land/groove combinations, sixteen powders and five primer combinations, the future of the 6.8 X 45 Kramer looks bright. This round currently offers almost the same performance as the 6.8mm SPC cartridge, and once development is complete will meet its performance, and when compared side by side with the 6.8mm SPC, the choice will be the 6.8 X 45 Kramer.

About David Crane

David Crane started publishing online in 2001. Since that time, governments, military organizations, Special Operators (i.e. professional trigger pullers), agencies, and civilian tactical shooters the world over have come to depend on Defense Review as the authoritative source of news and information on "the latest and greatest" in the field of military defense and tactical technology and hardware, including tactical firearms, ammunition, equipment, gear, and training.